All Our Yesterdays

Series: 'The Original Series'Episode Title: 'All Our Yesterdays'Episode Number: 323Synopsis: "When the ship visits a star about to go supernova, the crew learns that the entire population of its inhabited world have escaped into the planet's past. But Kirk accidentally steps through a time portal, and when Spock and McCoy try to retrieve him, they end up in an even earlier era, where Spock's savage Vulcan past reasserts itself."